Non-volatile memory has the advantage that stored data is not lost even when a power supply is interrupted. As a result, it is often used for storing data in systems, such as a personal computer (PC) basic input/output system (BIOS), a set top box, a printer, and a network server. Recently, non-volatile memory is being used in digital cameras and cellular phones.
One common non-volatile memory is an electrically erasable programmable read-only memory (EEPROM) type flash memory device capable of electrically erasing data in a memory cell in a lump manner or according to sector unit. During a programming operation for such a flash memory device, channel hot electrons from in a drain region to accumulate the electrons in a floating gate, thereby increasing the threshold voltage of a cell transistor.
During an erase operation, the flash memory device generates a high voltage between a source, substrate, and the floating gate to discharge electrons accumulated in the floating gate, thereby lowering the threshold voltage of the cell transistor.
With the rapid progress of high integration, the reduction of the cell size is needed. However, since it is difficult to secure a margin in a process, a further reduction is difficult to accomplish.